War and Peace and War: The Rise and Fall of Empires

by Peter Turchin

The bubonic plague was the most spectacular cause of the plunge in population, but by no means the only one. After all, the population decline began even before the plague struck in 1348. The other causes of population decline were famine, warfare, and falling birth rates. Furthermore, the Black Death was not a unique, unprecedented event in world history. Other spectacular epidemics, such as the Plague of Athens in 430 B.C., the Antonine plague (A.D. 165-180), and the plagues of Justinian (A.D. 542-546), always strike during the same phase of the secular cycle—at, or just past, the population peak. Less spectacularly, the bubonic plague staged a comeback during the next secular cycle in Europe, and played an important role in the population declines of the seventeenth century (for example, the Great Plague of London of A.D. 1665). In general, epidemics almost always play a role in secular population declines. The most important factor explaining the spread of epidemics during this phase of the cycle is increased mobility of people, resulting from the migration of landless peasants to towns and cities, increased vagrancy, and the movement of rebel bands and troops. Additionally, large segments of population are undernourished, or on the brink of starvation, and therefore become susceptible to disease agents. Thus, the conditions of overpopulation create a fertile ground for the spread of epidemics, and also ensure a high death toll.